The present invention relates to wires and wirebonding, and more particularly, to a method of wirebonding insulated wires.
An integrated circuit (IC) die is a small device formed on a semiconductor wafer, such as a silicon wafer. Such a die is typically cut from the wafer and attached to a substrate or base carrier for interconnect redistribution. Bond pads on the die are electrically connected to leads on the carrier via wire bonding. There is a continuing demand for more dense integrated circuits, yet without a corresponding increase in the size or footprint of the IC. There is also a desire for more inputs and outputs to ICs, resulting in high densities of connections between chips and their packages, and the need for fine pitch and ultra-fine pitch wirebonding. As the space between bond pads has decreased to accommodate greater numbers of bond pads, so to has the diameter of the bond wire. For example, 63 um pitch applications use 25 um diameter wire, while 52 um and 44 um pitch applications use 20.3 um diameter wire. Development is being done for a 37 um pitch application using 17 um diameter wire.
Decreases in wire diameter cause difficulties in handling and wirebonding. Parts that use smaller diameter wires tend to have higher wire sweep rejects at the molding stage, which can cause wires to short. Such wire sweep and shortings may be decreased by using insulated or coated wires. However, it is difficult to obtain good bonding quality when using coated wires, especially for the second bond. That is, a wirebonder makes a first bond at the device bond pad and a second bond at the carrier bond pad. Non-sticking on the second bond is a common problem with insulated wire.
The present invention provides a method of using a standard ultrasonic wirebonder that improves the bonding quality of the second bond, thus further enhancing the use of insulated wire for wirebonding applications.